Vibration isolation



Erz/fafa Hffshn Aug. 28, 1945...

s. H. HAHN VIBRATION ISOLATION Filed sept. 16, 1942 Patented Aug. 28, 1945 FFICE 2,383,645 VIBRATION ISOLATION Stuart H. Hahn, Williamsville, N. Y., assigner to The B. F. GoodrichvCompany, New York, N. Y., a corporation of New York Application September 16, 1942, Serial No. 458,588

11 claims. (C1. 24a- 358) 'Ihis invention relates to the isolation of vibration and is especially useful in isolating vibration in installations of machinesmr instruments, although the invention is useful in other springing arrangements, as well, including vehicle suspensions.

Itl has been found that generally rubber compositions having the characteristic of low hysteresis and therefore low damping ability have also a low tendency to creep or take permanent set under load, which is benecial in springing bodies. Again, compositions which have high hysteresis and therefore good damping ability exhibit a high tendency to creep or to take permanent set under load which is objectionable in load-supporting bodies. The qualities of low creep and good damping have not been available in the same composition, and have required compromise in selecting the'rubber composition for particular applications.

'Ilie principal objects of the invention are to provide a mounting structure having high vibration damping with low tendencyv to creep or to take permanent set, to combine the advantages of low and high hysteresis compositions in a single vibration damping installation, and to provide -for convenience of assembly and economy of manufacture. A further object is to provide for supporting the load by the main springing body while substantially relieving the damping body from the load.

These and other objects will appear from 'the following description and the accompanying drawing.

Of the drawing,

Fig. 1 is a perspective view of a shear type vibration isolating unit constructed according to and embodying the invention, parts being broken away, the unit being mounted under normal static load.

Fig. 2 is an end view thereof, partly broken away and partly in section and not under static load.

Fig. 3 is a side elevation, partly broken away and partly in section, of another form of the invention under normal staticload.

Fig.' 4 is an axial/section of the same without the supporting and supported members, and not under load.

Fig. 5 is a cross section thereof taken on line 5 5 of Fig. 4.

Fig'. 6 is a side elevation, partly in section, of

a modification of the invention.

Fig. 'I is a longitudinal section of a further, modification.

In accordance with the invention cushioning bodies of rubber or other suitable material of `or entirely and the other body is entirely or partly relieved of such load and is available for damping without the tendency of being subject to excessive creep. Y

Referring to the drawing, and first to the ,embodiment of Figs. 1 and 2- thereof, the numeral I0 designates a body, such as a machine frame, subject to vibration, and I I designates a supporting rail. The vibration isolating support comprises a metal plate I2 secured by bolts I3 to the body I 0, a supporting channel member It secured by bolts I5 to the rail II, an angle member I6 secured to the top flange vof the metal channel Ill by bolts I1, a body I8 of vulcanized resilient rubber or other rubber-like material having low hysteresis characteristics secured as by a vulcanized bond to the plate I2 and channel M and located therebetween, and a second body I9 of vulcanized rubber or other rubber-like material having high hysteresis characteristics .secured as by a vulcanized bond to the plate I2 and the angle I6 and located therebetween. In the unloaded position of the rubber bodies, or the position in which they are molded, a space 20 is provided between the bodies I8 and I9 and between the angle I6 and the channel It. The body I8 is preferably made of sufficient dimensions to support the entire static load in shear and when so loaded, the space 20 is closed. by distortion of the body I8 under shear load. The bolts Il are then inserted to clamp the angle I6 securely to the channel Ill with the body I8 loaded and the body I9 substantially without load. In the unloaded condition the bodies are held in a condition of opposing stress by the bolts Il. the body III is vibrated vertically both bodies I8 and I9 are subjected to shear loading and the bodyvl8 of low hysteresis characteristics principally supports the load while the body I9 of high hysteresis characteristics acts lto damp out vibration by absorption of energy due to hysteresis.

Referring to Figs. 3 to 5, the numeral 30 designates a machine'frame and 3l Va metal washer embedded in a concrete supporting floor 32. A hollow downwardly facing cup 33 is attached to the frame 30, 4as by bolts 34. The vibration isolating unit comprises asplit annular metallic When shell 35, a smaller metallic bushing 36 concentric therewith and a body 31 of rubber-like material therebetween and bonded thereto. A shorter split annular metallic bushing 39 having the same circumference as the bushing 35 is located therebelow and is bonded to a .second body 38 of rubber-like material which is also bonded to the bushing 36. The body 31 has low hysteresis characteristics and is preferably of suicient dimensions to sustain the entire static load whereas the body 38 is of high hysteresis characteristics and is used for damping vibration. Bushings 35 and 39 are forced into the cup 33 so as to compress the rubber bodies 31, 38 circumferentially. The load is supported in shear by bushing 36 and this may be threaded internally to adjustably received a leveling screw 40. The screw has a reduced end 4,'I adapted to engage the aperture of the washer 3|, and a polygonal head 42 whereby it may be rotated to adjust and level the machine;

In forming the vibration isolating unit, a space 44 is provided between bushings 35 and 33 and the bodies 31 and 38 so that when the unit is placed under lthe static load, the load may be assumed by the body 31 and deflection thereof may occur under such load before the bushing 35 is brought into contact with` bushing 39. If the load is lifted, the bodies Will be in a condition of Opposing stress.

In the form of the invention shown in Fig. 6, the supporting surface is designated by the numeral 50 and the supported machine by the numeral 5I. The machine is supported in shear by a plurality of vibration isolating units 52, 53, 54, 55. Each of the units 52, 54 comprise an outer bushing 56 of metal, an inner bushing 51 of metal and an`annular body 58 of soft rubberlike material having a low hysteresis characteristic therebetween andl bonded thereto, an ad-l justing screw 59 supporting the inner bushing from the supporting surface 50.

Each of the units 53, 55 comprises an outer bushing 60 of metal, an inner bushing 6l of metal and a body 62 of soft rubber-like material having a high hysteresis characteristic is located therebetween and bonded thereto, an adjusting screw 63'being threaded to engage the inner bushing and support it from the supporting surface 50. The arrangement is such that some of the'isolating units are of rubber-like material having a low hysteresis characteristic and adopted fully to support the static load in shear, and the-others are of rubber-like material having a high hysteresis characteristic and adopted to damp vibration by shear loading. While the bushing type of isolating unit is shown, units of at shear type somewhat like the unit of Fig. 1 may be used, if desired.

`The invention is applicable also to mountings or springs of the circular shear or torsion type, as in the embodiment of Fig. '1, which is sultable, for example, for use as a. spring in a vehicle suspension. A central shaft has vulcanized upon it a cylindrical body 1l of rubber composition of low hysteresis type which is securedas by a vulcanized bond t an outer shell 12, preferably split so as to be compressible into an outer sleeve or housing 13 in a manner such that rotation of the shaft and housing, one with respect to the other, is resisted by the body 1I in circular shear. For damping the springing ac'- tion a second cylindrical body 14 of high hysteresis material is mounted upon the shaft 10 and within the housing 13. The body 14 may have inner and outer sleeves 15 and 16 secured to-it as by a vulcanized bond, so as to facilitate introduction of this body into the assembly after the springing body 1| has been inserted and preferably while body 1I is stressed in rotation to its normal load position, in which position the body 14 is-secured in place in an unstressed condition or substantially so. This operationcan be carried out during manufacture of the spring, in which case the bodies will oppose each other in stress, or-during mounting of the spring in the vehicle or-other structure, and has the result, as hereinabove discussed with reference to the4 other illustrated embodiments, of permitting the main springing body to relieve the other body of load-supporting stress so that the second body can serve in its damping capacity without being subject to objectionable creep.

In all the illustrated embodiments of the invention the low hysteresis rubber-like composition is preferably of soft vulcanized natural rubber composition, although some synthetic compositions are suitable, in` the characteristic of having little tendency to creep or to assume permanent set. The high hysteresis rubber-like composition is preferably a natural or synthetic rubber composition or of polymerized vinyl chloride material, Thiokol" material or other suitable rubber-like composition having high hysteresis, as such materials have been found superior to natural rubber compositions for damping yibrations while inferior to natural rubber compositions for supporting a load because they have considerable creep or permanent set.

The combination of high hysteresis material and low hysteresis material ina single installation provides the high vibration damping properties of one and 'the high resistance to permanent set of the other and provides for absorption and damping of vibration over a broader band of frequencies than would be possible where only one of the materials is employed. This is particularly true where the initial stress of the low hysteresis material is suilicient to carry the entire static load so that the damping material is relieved of such load.

Variations can be made without departing from the scope of the invention as it is defined by the following claims.

I claim:

1. Vibration-isolating apparatus comprising a load-supporting body of rubber-like material having a low hysteresis characteristic for sustaining a load from a support, and a body of rubber-like material having a high hysteresis characteristic for damping vibrations between the load and its support, and means for mounting said bodies between the load and its support in vibrationreceiving relation thereto, including means for mounting said body of' low hysteresis under loadbody of high hysteresis inrelation to be substantially relieved of the load.

3. Vibration-isolating apparatus comprising relatively movable fiat plate-like members for the support of a load, a body of rubber-like material having a low hysteresis characteristic located for shear loading between said members and secured thereto, and a body of rubber-like material having a high hysteresis characteristic also located between said members and secured thereto.

4. Vibration-isolating apparatus comprising a shear mounting having relatively movable members for the support of a load, and rubber-like bodies arranged between said members for shear distortion `and bonded thereto, said bodies comprising a body of material having low hysteresis characteristics and a body of material having 8. Vibration-isolating apparatus as defined in relatively movable structures for the support of a load, a load-supporting body oi.' rubber-like material interposed between said structures and secured thereto, and a damping body of flexible material interposed between said structures and secured thereto, said bodies being mounted in such relation to the structures that when the loadsupporting body is in load-'supporting condition it substantiallyrelieves the damping mounting from such load.

l'1. Vibration-isolating apparatus as deiined in claim 6 in which said bodiesare mountedfor movement of said structures through shear stress of said bodies.'

claim 6 in which said bodies are mounted for movement of said structures through shearA stress of said bodies, and the portions of said bodies at one of said structures are mounted in a condition of opposing stress.

9. Vibration-isolating apparatus as defined in claim 6 in which said bodies are mounted for movement of. said structures through shear stress of said bodies, and one of said structures comprises rlatively movable parts and meansv for holding said parts in positions for opposing stress of said bodies. f

10. A resilient vibration-isolating mounting comprising a load-transmitting member. a body of rubber-like material secured to said member and projecting therefrom, a second body of rubber-like material of higher hysteresis characterisitc than the first disposed to one side of the first said body and secured to said member and projecting therefrom, and' load-transmitting means including elements secured to and connecting the projecting bodies. in a manner to 1m-e pose less load on the said second body than on the iirst said body while vibration is transmitted to both bodies. l 11. Vibration-isolating apparatus for sustaining a load from a support comprising a loading structure, a supporting structure, a body of rubber-like material secured to said structures and having a low hysteresis characteristic for supporting the loading structure from the supporting structure by shear loading of said body, and a body of rubber-like material secured to said 'structures and having a high hysteresis characteristic for damping vibrations by shear stressing thereof between the loading and supporting structures. STUART H. HAHN. 

